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In contrast to dogs, blood loss anemias are less commonly observed in cats, albeit they happen with trauma and surgery. In fact, many cats drop their PCV during and shortly after surgery which may in part be blood loss, but also unexplained lysis and sequestration. Moreover, external blood loss can rapidly result in iron deficiency particularly in the very young kitten (even with repeat phlebotomies for diagnostic purposes), however, the classic microcytosis and hypochromasia in iron deficiency may be very difficult to appreciate due
to small feline red cells. The most common reason for blood loss is flea infestation, while maggots, ticks, and hookworms are less likely leading to major blood loss. Skin and other tumors may also cause local bleeding. Blood loss anemias are generally regenerative after 3-4 days and remain regenerative even when iron deficient. While in the above cases hemorrhage was caused
by vascular injury, there are also a variety of bleeding disorders to consider.
Thrombocytopenia is rare in cats but may be induced by drugs (methimazol) and rarely infection and cancer; immune-mediated thrombocytopenia also seems to occur rarely. Accurate platelet counts can be difficult to obtain due to their large size platelets and tendency to aggregate. Thus, any platelet count needs to
be confirmed with an estimate from a blood smear examination (20,000 platelets/μl equals 1 platelet seen on a high power microscopic field). Thrombopathia – impaired platelet function - may be triggered by aspirin or similar drugs (cats appear particularly sensitive
to platelet injury but less likely to aspirin or steroidal ulceration). Hereditary thrombopathias are extremely rare. Compared to dogs, anticoagulant rodenticide poisoning is less commonly observed in cats. However, coagulopathies due to hepatic failure are much more severe in cats than dogs; hence diagnostic liver biopsies are frequently associated with serious hemorrhage. Furthermore, there are several hereditary coagulopathies such as hemophilia A and B in domestic and Himalayan cats as well as a vitamin K-dependent coagulopathy in Devon Rex and Sphinx cats. Interestingly, domestic and exotic shorthair cats often have a coagulation factor
XII deficiency; while this causes a markedly prolonged partial thromboplastin time, this is not associated with
a bleeding tendency. Generally, the prothrombin and partial thromboplastin times provide sufficient information to differentiate the coagulopathies, although specific factor analyses may be needed.
Hemolytic anemias in cats are often hard to recognize as the degree of bone marrow regeneration and the evidence of bilirbinuria and hyperbilirubinemia are often mild (any bilirubinuria is important in a cat). In fact, icterus in cats is much more likely due to hepatic failure. While the normal feline spleen is very small, it can get fairly enlarged in cases of hemolytic anemia. Furthermore there is a syndrome of increased erythrocytic osmotic
fragility seen in Abyssinian, Somali and other domestic house and purebred cats with massive splenomegaly. Pyruvate kinase deficiency is a common hereditary disease causing intermittent hemolytic anemia in Abbysinnian, Somali and other purebred and even domestic house cats. There is also porphyria, a heme synthesis defect, which causes hemolysis but most remarkably erythrodontia with fluorescing teeth. Porphyria may dominantly or recessively inherited and cats may live for years with this condition requiring no specific treatment.
In contrast to dogs, primary (auto-) immune-mediated hemolytic anemia seems rare in cats, but may be seen with other triggers such as infections, drugs, and cancer (secondary IMHA). Their species-specific Coombs’ test is positive. In addition, some show autoagglutination that may break up when adding saline (Rouleaux) and after washing with saline when caused by unspecific agglutination such as by EDTA. More important than primary IMHA is alloantibody associated hemolysis. Neonatal type A and AB kittens nursing from a type B queen will frequently develop acute hemolysis of the newborn during the first hours to days of life. Classic signs are acute death, massive pigmenturia due to hemoglobinuria and occasionally they may develop icterus and a tail tip necrosis and survive. Similarly important are A-B mismatched (first transfusion due to preformed antibodies and rarely others like Mik and only after prior sensitizing) acute hemolytic transfusion reactions. Thus AB typing is critical prior to breeding and transfusing cats. Transfusing canine blood to cats (xenotransfusion) causes always severe hemolytic reactions and is not recommended.
Feline hemolytic anemias
· Infections
· Mycoplasma hemofelis, (also hemominutum, turice- sis)
· Cytauxzoon felis
· Feline Leukemia Virus infection (A type)
· Feline Infectious Peritonitis
· Immune
· Alloimmune – neonatal isoerythrolysis and acute transfusion reactions
· Autoimmune or primary hemolytic anemia (rare com- pared to dogs)
· Secondary (drugs [methimazol], infection, cancer)
· Toxic
· Drugs - acetaminophen, lidocaine spray, propofol, etc.
· Onions
· Metabolic
· -Hypophosphatemia (D. mellitus, hepatopathy, hyper- alimentation)
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